The terrible winter weather
The Battle of Stalingrad.
You did not designate the options for this answer. I can tell you that Old Man Winter was the number one thing that halted the Nazis from advancing across the Soviet Union. Their military vehicles and people could not get through the deep and extremely cold snow and in the spring the mud was a significant factor in slow mobility. The Nazis did not have clothing and boots that could hand the many degrees below zero temperatures and their equipment could not either.
Another constant problem for the Nazi troops in the Soviet Union was the inability of the German leaders to keep the troops supplied during the winter and other times too due to the long distances from Germany to the Soviet Union.
Another factor was the Russian tanks and planes held them at bay.
Several factors contributed to the Soviet Union being able to stop the German invasion, called Operation Barbarossa.
First, Hitler and the German High Command underestimated the strength of the Soviet troops and the number of reserves the Soviets could call up. They also underestimated the number of tanks, airplanes, and other war machinery that the Soviets had, although much of the machinery was old or in poor repair. Hitler and his advisors also wasted time by arguing about the course they should follow. They also thought that the Soviet Regime would collapse from lack of domestic support.
The Soviet policy of scorched earth also affected the German invasion. As the Germans advanced, the Soviets burned crops, destroyed bridges, dismantled and moved steel and munition plants, evacuated factories, and destroyed or moved railroad cars (Germain railroad cars used a different gauge of track that that of the Soviets, so they could not use German rail cars on Soviet tracks). As the Germans advanced into Russia, it became more difficult to keep the troops supplied.
Weather was another important factor. Rains in July turned the sandy Russian roads into mud, slowing the transport vehicles which traveled behind the German tanks. In October, during the Battle of Moscow, the weather turned to rain and then to snow and sub zero temperatures. The German troops were ill-prepared to fight in the cold weather, with no provisions of winter clothing, and the cold affecting the Germans’ mechanized transport, tanks, artillery, and aircraft. The Soviets were well provided for in the cold weather and fought more effectively in the cold weather than the Germans. Added to the cold weather was the fact that the German troops were tired and the number of troops began to decline with no new troops sent to replace them.
The terrible winter weather
The German invasion of the Soviet Union in 1941 succeeded in part because they attacked with no warning. The Soviet Union didn't have time to react to the German army's invasion.
The German invasion of the Soviet Union during WW2 was called Operation Barbarossa.
Germany : Operation Barbarossa was the German invasion of Russia .
The Battle of Stalingrad was a disaster for the German Armies
The terrible winter weather
The German invasion of the Soviet Union in 1941 succeeded in part because they attacked with no warning. The Soviet Union didn't have time to react to the German army's invasion.
Operation Barbarossa
June 22. 1941
It stopped when Germany launched Operation Barbarossa, which was the Nazi invasion of the Soviet Union.
The invasion of the Soviet Union had to specifically start in June, at the beginning of summer, as the extreme Soviet winters would have made an invasion impossible.
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barbarosa
The German invasion of the Soviet Union during WW2 was called Operation Barbarossa.
Germany : Operation Barbarossa was the German invasion of Russia .
The soviet union survived the invasion because they had enough people and resources to continue to fight. The leaders had no care for the people they were loosing in the war, and they were able to keep their industrial force by disassembling factories and moving them farther into the soviet union.
Besides Germans also people from Austria and former Czechoslovakia.